import java.util.Scanner;
//递归求 1 + 2 + 3 + ... + 10
public class Sum2 {
    public static int sum(int n) {
        if(n == 1) {
            return 1;
        } else {
            return n + sum(n - 1);
        }
    }
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        System.out.println(sum(n));
    }
}
